60 research outputs found
Hyperbolic heat equation in Kaluza's magnetohydrodynamics
This paper shows that a hyperbolic equation for heat conduction can be
obtained directly using the tenets of linear irreversible thermodynamics in the
context of the five dimensional space-time metric originally proposed by T.
Kaluza back in 1922. The associated speed of propagation is slightly lower than
the speed of light by a factor inversely proportional to the specific charge of
the fluid element. Moreover, consistency with the second law of thermodynamics
is achieved. Possible implications in the context of physics of clusters of
galaxies of this result are briefly discussed.Comment: 14 pages, no figure
On the inertia of heat
Does heat have inertia? This question is at the core of a long-standing
controversy on Eckart's dissipative relativistic hydrodynamics. Here I show
that the troublesome inertial term in Eckart's heat flux arises only if one
insists on defining thermal diffusivity as a spacetime constant. I argue that
this is the most natural definition, and that all confusion disappears if one
considers instead the space-dependent comoving diffusivity, in line with the
fact that, in the presence of gravity, space is an inhomogeneous medium.Comment: 3 page
On the gravitational instability of a dissipative medium
This paper shows that the ordinary Jeans wave number can be obtained as a
limiting case of a more general approach that includes dissipative effects.
Corrections to the Jeans critical mass associated to viscosity are established.
Some possible implications of the results are finally discussed.Comment: 5 pages, RevTe
The Simple Non-degenerate Relativistic Gas: Statistical Properties and Brownian Motion
This paper shows a novel calculation of the mean square displacement of a
classical Brownian particle in a relativistic thermal bath. The result is
compared with the expressions obtained by other authors. Also, the
thermodynamic properties of a non-degenerate simple relativistic gas are
reviewed in terms of a treatment performed in velocity space.Comment: 6 pages, 2 figure
Some thoughts about nonequilibrium temperature
The main objective of this paper is to show that, within the present
framework of the kinetic theoretical approach to irreversible thermodynamics,
there is no evidence that provides a basis to modify the ordinary Fourier
equation relating the heat flux in a non-equilibrium steady state to the
gradient of the local equilibrium temperature. This fact is supported, among
other arguments, through the kinetic foundations of generalized hydrodynamics.
Some attempts have been recently proposed asserting that, in the presence of
non-linearities of the state variables, such a temperature should be replaced
by the non-equilibrium temperature as defined in Extended Irreversible
Thermodynamics. In the approximations used for such a temperature there is so
far no evidence that sustains this proposal.Comment: 13 pages, TeX, no figures, to appear in Mol. Phy
Simultaneous adsorption of quinoline and dibenzothiophene over Ni-based mesoporous materials at different Si/Al ratio
Possible experiment to check the reality of a nonequilibrium temperature
An experiment is proposed to check the physical reality of a nonequilibrium absolute temperature previously proposed from theoretical grounds in the framework of extended irreversible thermodynamics
Gravitational instability of a dilute fully ionized gas in the presence of the Dufour effect
The gravitational instability of a fully ionized gas is analyzed within the
framework of linear irreversible thermodynamics. In particular, the presence of
a heat flux corresponding to generalized thermodynamic forces is shown to
affect the properties of the dispersion relation governing the stability of
this kind of system in certain problems of interest.Comment: 8 pages, 2 figure
The thermal and kinematic Sunyaev-Zel'dovich effects revisited
This paper shows that a simple convolution integral expression based on the
mean value of the isotropic frequency distribution corresponding to photon
scattering off electrons leads to useful analytical expressions describing the
thermal Sunyaev-Zel'dovich effect. The approach, to first order in the Compton
parameter is able to reproduce the Kompaneets equation describing the effect.
Second order effects in the parameter induce a slight
increase in the crossover frequency.Comment: 7 pages, 2 figure
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